Ramarge3653 wrote:... but I've been reading a lot of forum posts and some say to swap the stock 6922 tube for a Seimen 7308 and the hiss will be almost non existant.
A bit more research reveals 7308 is a 1962 ECC188 equivalent, described in the spec as "long life shock and vibration resistant double triode with anti-microphonic construction."
Spec is here http://www.drtube.com/datasheets/e188cc-philips1962.pdf
Spec noise equivalent resistance for the ECC188/7308 is 250R, versus 300R for a standard ECC88. That's not going to set the world alight by way of improvement. So, by spec, there's not much in it as to broad spectrum hiss performance. But microphonics will be better, though I've never noted that in an ECC88. Perhaps as Hanuman posts, because of its location in the path. Also, the noise Hanuman describes when ECC88 used as an MC first stage sounds like non-ideals anyways perhaps, and not part of theoretical or spec figures perhaps. Desciption seems like flicker noise, which has a strong lf bias, and crackle.
I never knew about ECC188s, so that's a discovery. Not sure I'd be at the front of the line to try, in this case, on paper though there's not much advantage unless microphony is a problem. But, you never know and there may be non-ideals in play too. Cheap and plentiful they certainly aren't !
I agree with hanuman, upstream seems the place to look for noise improvements.